Next time you're about to tell someone you can't do something, stop yourself. Try saying, "I can't do that—yet" instead, which may go a long way in terms of how you view yourself and your abilities, according to Stanford University psychologist Carol Dweck, Ph.D.

This tiny word has a big impact. Dweck has done a whole lotta research about having a fixed mindset versus a growth mindset. If you think you just are the way you are, and your abilities are what they are, then you'll think your lot in life is what it is: unchangeable and inevitable. This is a fixed mindset.

On the flipside, if you have a growth mindset, then you are open and ready for improvement. You're allowing room for advancement, learning and positive change in your life. And you can change your attitude daily simply by adding "yet" to your statements.

According to the Science of Us, from the perspective of a teacher and a student, Dweck explains it like this: "We've found that putting in certain phrases like not yet or yet can really boost students' motivation. So if a student says, 'I'm not a math person—*yet,**' '*I can't do this—yet.' And it means that with your guidance they will continue on their learning trajectory and get there eventually. It puts their fixed mindset statement into a growth mindset context of learning over time."

And honestly, that's the way it should be. You are never so old that you stop growing and evolving, that you can't learn new habits and improve your well-being. You should constantly be striving to improve... so get motivated to get better in 2015 about your fitness routine, your career goals, your diet, anything and everything.

You're not the best you can be yet. Looks like we just found our new favorite mantra.